1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and a method for transmitting control information of a small base station that operates in a Low Duty operation Mode (LDM) to a terminal.
2. Description of the Related Art
A wireless communication system may provide a femto cell service for providing a high-speed data service while solving a service problem of a propagation shadow area. The femto cell denotes a small cell area formed by a small base station accessing a mobile communication core network via a broadband network installed in an indoor space such as an office and a household. Here, the small base station denotes a base station of small power that a user installs in person, and includes any or all of a micro base station, a self configurable base station, a compact base station, an indoor base station, a home base station, and a femto base station. In the following description, it is assumed that the small base station is a femto base station.
The femto base station operates in a normal operation mode or a Low Duty operation Mode (LDM). For example, in a case where terminals that access the femto base station operate in an idle mode or a sleep mode, or a terminal that accesses the femto base station does not exist, the femto base station operates in the LDM in order to reduce interference for neighboring cells. At this point, an LDM section where the femto base station operates in the LDM is divided into an Available Interval (AI) during which the femto base station transmits control information, and an UnAvailable Interval (UAI) during which the femto base station does not transmit a signal.
A terminal of a cellular system may recognize a base station based on a preamble or broadcast control information transmitted by the base station, and try a cell selection to the base station. However, in a case where the femto base station enters an UAI, the femto base station does not transmit a signal. Accordingly, the terminal cannot recognize the femto base station that has entered the UAI. For example, when a user turns on power of a terminal at a position adjacent to a femto base station that has entered an UAI, there is a problem since the terminal cannot recognize the femto base station even though the terminal is adjacent to the femto base station and so the terminal attempts to access a macro base station. In another example, a terminal that operates in an idle mode cannot recognize the femto base station and so it cannot perform a position update. In a further example, during a handover, the terminal cannot scan the femto base station that has entered a UAI.
Another problem is that overhead may occur when a macro base station including the femto base station transmits information regarding an operating mode of the femto base station to a terminal so that the terminal may search for the femto base station that has entered a UAI.
Therefore, a need exists for a system and method for transmitting information of a femto base station that operates in a LDM in a wireless communication system.